Investigators are "90% sure" the noise heard on the black box of a Russian airliner seconds before it crashed was caused by a bomb.

"The indications and analysis so far of the sound on the black box indicate it was a bomb," a member of the air accident investigation team in Egypt told Reuters.

It comes a day after Egyptian investigators said a "spectral analysis" of the "nature of the noise" on the flight recorder was underway.

The US and Britain previously said an explosive device is likely to have brought down the Metrojet flight last Saturday, which a group affiliated with Islamic State has claimed responsibility for.

Security at Sharm El Sheikh airport has become a widespread concern since the crash with the UK, Russia and various other countries suspending flights from the Red Sea resort.

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Seven officials told the Associated Press the airport had long suffered from security gaps including a malfunctioning key baggage scanning device, lax searches at an entry gate for plane food and fuel and bribe-taking by policemen.

They described how poor paid policemen monitoring X-ray machines often took bribes for as little as 10 euros to let through "a bag full of drugs or weapons".

They added that bosses had failed to replace a faulty scanner in the sorting area for checked-in bags - an issue that had been raised in security reports.

One said the machine was unplugged to save power at times and even when it was working was only used to scan a sample of bags.

Another official said the staff made sure the scanner was operating well enough whenever international experts came to review measures at the airport.

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The officials also revealed full searches weren’t always carried out at the entry gates where food is delivered directly to some planes by local hotels, either because guards know the delivery men or have been bribed with meals.

A retired senior official from Egypt's Tourism Ministry, Magdy Salim, said guards regularly skip security checks for friends and co-workers and often didn't search people "out of respect to save their time if they look chic or if they come out of a fancy car".

"Airport security procedures in Egypt are almost (all) bad" and marred by "insufficiencies", Mr Salim said.

A spokesman for Egypt’s Aviation Ministry dismissed the claims saying "Sharm El Sheikh is one of the safest airports in the world", while the Egyptian President previously said a British security team was satisfied with the airport after a visit 10 months ago.

British Foreign Secretary Philip Hammond said the incident could lead to changes in flight security.

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"If this turns out to be a device planted by an ISIL operative or by somebody inspired by ISIL, then clearly we will have to look again at the level of security we expect to see in airports in areas where ISIL is active," Mr Hammond told the BBC.

Emirates Airlines President Tim Clark said on Sunday he expected the crash would result in demands for stringent aviation security worldwide.

Meanwhile, British tourists trying to get back to the UK supported the claims saying airport security was "shocking", even after the disaster, with officials allowing travellers to pay to be fast-tracked past airport scanners.

Some 1,936 passengers returned to the UK from Sharm on Sunday, bringing the total number so far to 5,298.

Travel writer Simon Calder told Sky News that there was "extreme frustration" among the airlines and tour operators about how slow the operation is.

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He said tour operators would meet on Monday to decide whether to scrap all holiday flights and packages to Sharm in light of the security chaos.

Egyptian authorities have begun checking CCTV and questioning the airport staff and ground crew who prepared the Metrojet flight before take-off with some employees under surveillance.